Autogyro aircraft are a form of powered or unpowered rotorcraft, typically having one or more auto-rotating airfoils or blades. Gyrodynes power the rotor in preparation for takeoff, and then fly with a freewheeling rotor (rotary wing) in flight, pushed by a pusher propeller. Helicopters power the rotary wing with an onboard engine. Various versions of these have been developed since the first quarter of the twentieth century. During the 1930's autogyro aircrafts were actually employed commercially as rotary wing aircraft for shuttling mail.
An autogyro develops lift from unpowered, freely rotating, rotary blades. The blade of an autogyro is a wing. The wing rotates or “windmills” in response to wind passing through the blade or wing from the underside thereof. As wind passes through the underside of the blade, the angle of the blades with respect to the wind results in the blades responding as sails, transferring momentum from the wind into the blade, turning the blade, and diverting the wind. As the wind is diverted, momentum corresponding to the change in direction and speed of the wind is transferred as momentum into the movement of the blade or wing.
The key principle of an autogyro is the knowledge that the windmilling process of rotating the rotary wing or blades of an autogyro is sufficient to develop speed sufficient to invoke Bernoulli's principle. If the blade is made as more than a windmill, the blade may have a comparatively flatter undersurface and a rounded airfoil shape on its upper surface. Accordingly, as the blade moves through the air, under the motivation of the wind passing through the blade from underneath the blade, the airfoil develops a reduced pressure along the upper surface thereof, developing lift to raise the blade.
A fixed wing aircraft is drawn through the air by a propeller, thus passing air over the fixed wing. Lift occurs by the drop in pressure that occurs as the wind flowing over the top of the wing accelerates to pass over the thickest portion of the wing. A rotary wing also develops lift by the relative motion of air or wind over the top thereof.
The drop in pressure results from the principles of conservation of energy as the air moves relative to the airfoil. Its total pressure head remains substantially constant. If the velocity changes, as it must in order to speed up to pass through a reduced cross sectional area of flow, then the static pressure must drop in order to maintain head at a substantially constant value.
The curvature of the upper surface of an airfoil restricts the available cross sectional area for the air movement to pass through, requiring the air to speed up, thus reducing its pressure to meet conservation of energy requirements.
Autogyro aircraft have been motivated by pusher propellers mounted near the rear of a fuselage, pushing the aircraft forward. The rotor disk, that is, the theoretical disk is swept by the rotary wing, is pitched at an angle that passes the incoming air up through the rotor disk. The rotor disk is tilted upward towards its front extremity, and comparatively downward at its rear most extremity. Meanwhile, the actual angle of the blade itself with respect to the air through which the blade passes in its rotary motion, is set at some angle that will tend to minimize drag, while maximizing lift. “Blade pitch” is generally controlled or set at a position to “fly” through the air.
The most significant discovery about autogyro aircraft is probably the fact that the relative airspeed of a blade or wing rotating in air may be uncoupled from the relative air speed of the overall system (fuselage, axis of rotation, or the like). Thus stall speed may be substantially different from relative ground speed.
Helicopters can actually hover. Autogyros, on the other hand, can only hover in certain limited circumstances wherein their forward motivation from a motor or other mechanism is matched by an actual head wind speed relative to the earth that is naturally occurring. In this circumstance or while descending, an autogyro may hover or maintain position with respect to the earth. Nevertheless, a helicopter may hover in substantially any relative wind, including a still air situation.
Wind energy has been developed along a path substantially independent from aircrafts for many years. Momentum from the passing wind is received, the wind is redirected and that momentum is harvested into motion of the windmill.
By appropriate mechanical linkages, a windmill may pass energy as a linear translation or as a rotary motion to some other operational mechanism. For example, a gristmill transfers the energy of the wind, vanes or blades of the mill to the rotatory motion of a grinding stone.
In the early twentieth century, generators, operating largely as windmills were installed at remote locations inaccessible by public utilities. Such system relied on a windmill-like blade or multiple blades turning a generator, storing energy in batteries.
In more recent years, towers have been erected in various configurations supporting blades that reflect all the aerodynamic engineering of aircraft wings and aircraft propellers acting to retrieve energy from the wind, rather than drawing an aircraft or pushing an aircraft through the air. Thus, large systems have been developed at substantial cost to elevate wind turbine blades, propellers, or the like above the surface of the earth in areas of high wind, constant wind, or otherwise commercially feasible locations of wind energy available for harvest.
Nevertheless, wind energy has been difficult and expensive to develop. Wind on the surface of the earth is predictable primarily as weather patterns, or as daily, directional breeze. At a particular location the daily cycle of wind velocity and direction as a function of time may be plotted. Substantial effort, energy, and engineering resources have been devoted to development of meteorological towers and instrumentation developed to test wind velocity and direction, near the surface of the earth. Wind is created by, and therefore dependent on, terrestrial phenomena. For example, canyons are a classic source of wind energy. The diurnal cycles of heating and cooling along canyons, mountains, and the like give rise to wind velocities and directions that may be harvested for wind energy.
Nevertheless, the physical structures available, and the methods of installing them, are limited by the physics and engineering available to exploit them. There is thus felt a need to develop a method and apparatus to capture wind energy using a greater duty cycle than is typically available for terrestrial windmill locations and effectively use it for generating power.